1. Field of the Invention
Embodiments of the present invention are directed in general toward high performance photoresist compositions used in conjunction with eximer laser and electron beam lithography sources. Specifically, the photoresist compositions of the present invention include diamondoid derivatives having polymerizable and hydrophilic-enhancing functionalities. The diamondoids of the present invention include lower diamondoids such as adamantane, diamantane, and triamantane, as well as the diamondoids tetramantane, pentamantanes, and higher compounds.
2. State of the Art
Increasing demands for devices with higher circuit densities have led to the use of shorter wavelength light sources in optical lithography. KrF (krypton fluoride) excimer laser lithography operating at a wavelength of 248 nm has has been used for the production of devices having feature sizes ranging from 0.25 to 0.13 microns. Rapid advances in the miniaturization of microelectronic devices, and demands for devices with increasingly greater circuit densities, are requiring the development of new, imageable polymeric photoresist materials to be used with ArF (argon fluoride) excimer laser lithography at 193 nm, and there is a need on the horizon for resist materials which can operate in the extreme ultraviolet and soft x-ray regim. According to The National Technology Roadmap for Semiconductors, (Semiconductor Industry Association, San Jose, Calif., 1997), the next most likely candidate is an F2 source operating at 157 nm.
Conventional g-line (436 nm) and i-line (365 nm) photoresists are well-balanced in terms of high-resolution, high sensitivity, and good dry etch resistance, but they typically comprise a novolac base resin and a diazonaphthoquinone PAC (photoactive compound), both of which contain a phenolic moiety that absorbs light having wavelengths below about 365 nm. Thus, the phenolic based resists cannot be used in these shorter wavelengths regimes, such as those found in ArF lithography, because they are completely opaque at 193 nm. The incident radiation cannot penetrate through the full thickness of the resist. This is a significant issue at 248 nm (KrF), which is the wavelength used for 0.25 micron and 0.18 micron generation devices.
Photoresists are materials used to transfer an image onto a substrate. A layer of the photoresist (or “resist”) is formed on a substrate, and then exposed through a mask to a source of radiation. The mask has some regions that are opaque, and some regions that are transparent to the radiation. The portions of the photoresist that are exposed to the radiation undergo a chemical transformation such that the pattern of the mask is transferred to the photoresist layer, which after development provides a relief image that can be used to selectively process the underlying substrate.
In general, a photoresist composition comprises at least a resin binder and a photoactive agent. The “chemically amplified” resists in use today were developed for the formation of sub-micron images and other high performance applications. They may be either positive or negative acting. In the case of a positive acting resist, the regions that are exposed to the radiation become more soluble in the developer, while those areas that are not exposed remain comparatively less soluble in the developer. Cationic initiators are used to induce cleavage of certain “blocking groups” pendant from the photoresist binder resin, or cleavage of certain groups that comprise a photoresist binder backbone. Upon cleavage of the blocking group through exposure of a layer of photoresist to light, a base soluble functional group is formed, such as a carboxylic acid or an imide, which results in a different solubility in the developer for the exposed and unexposed regions of the resist layer.
As taught by J. D. Plummer et al., in “Silicon VLSI Technology” (Prentice Hall, Upper Saddle River, N.J., 2000), pp.221-226, deep ultraviolet (DUV) resists in use today are not modified novolac resists. Deep ultraviolet (DUV) photoresist materials in use today are based on chemistry that makes use of a phenomenon called “chemical amplification.” Conventional resist materials that were designed to operate at 365 nm and 248 nm achieved quantum efficiencies of about 0.3, meaning that about 30 percent of the incoming photons interacted with the photoactive compound to expose the resist.
DUV resists, according to Plummer, work on a different principle that is illustrated in FIG. 1. Referring to FIG. 1, incoming photons react with a photo-acid generator (PAG) 101, creating an acid molecule 102. Acid molecules 102 act as catalysts during a subsequent resistant bake to change the properties of the resist in the exposed region. The photo-acid generator 101 initiates a chemical reaction that makes the resist soluble in a developer in a subsequent developing step that occurs after exposure to the radiation. The reactions are catalytic and the acid molecule 102 is regenerated after each chemical reaction and may therefore participate in tens or even hundreds of further reactions. This is what allows the overall quantum efficiency in a chemically amplified resist to be much larger than 1, and is responsible for improving the sensitivity of a chemically amplified resist from the previous values of about 100 mJ cm−2 for conventional diazonaphthoquinones to the current values of about 20-40 for the new chemically amplified the ultraviolet photoresists.
The principle of a chemically amplified photoresist is illustrated in FIG. 1. Referring again to FIG. 1, photoresists of the present intention included in general a photo-acid generator 101 and a blocked or protected polymer 103 which is insoluble in the developer because of attached molecules 104 (labeled additionally “INSOL” in FIG. 1). Incident deep ultraviolet photons interact with the photo-acid generator 101 to create an acid molecule 102. The spatial pattern of the acid molecules 102 within the resist create a “stored,” or latent image of the mask pattern. After exposure, the substrate undergoing processing is baked at a temperature of about 120 degrees C. in a process called post exposure bake (PEB). The heat from the post exposure bake provides the energy needed for the reaction between the acid molecules 102 and the insoluble pendant groups 104 where the reaction is to take place. The heat from the post exposure bake provides the energy needed for the reaction between acid molecules 102 and the insoluble pendant groups 104 attached to main polymer chain 103; the heat from the post exposure bake also provides diffusion mobility for the acid molecules 102 to seek out unreacted pendant groups 104, the essence of the catalytic nature of this reaction.
During the post exposure bake, the insoluble pendant groups 104 are either converted to soluble pendant groups 105, or cleaved from the polymer chain 103. In either case, the insoluble, blocked polymer is converted to an unblocked polymer as soluble in an aqueous alkaline developer.
The polymers that comprise the chain 103 may comprise such polymers as polyamides, polyimides, polyesters, and polycarbonates since these are easily processed, mechanically strong, and thermally stable, and thus have become important materials in the microelectronics industry. Introduction of polycyclic hydrocarbon substituents, including alicyclic rings and other caged hydrocarbons, have been shown to impart greater solubility and enhanced rigidity, improving the mechanical and thermal properties of the resulting polymers. Previous studies have involved the introduction of adamantyl groups into 193 nm resists, but to the applicant's knowledge, there have been no previous attempts to incorporate any diamondoid compound higher than adamantane into the base resin structure. These composition may incorporate lower diamondoids such as diamantane and/or triamantane into the resist structure, or they may include diamondoids such as tetramantane and higher.
In many instances, the use of photoacid generators that produce weaker photoacids and resists compositions that require lower post exposure bake (PEB) temperatures, such as 110° C. or less, would represent a significant advantage. For example, if the desired deprotection chemistry could be carried out with a weaker acid, a wider range of photoacid generators could potentially be employed. Moreover, the industry continually seeks use of lowered post exposure bake temperatures because of uniformity considerations.
Thus, it would be advantageous to have new photoresist compositions, particularly positive acting photoresist compositions, that may be effectively imaged in the sub-200 nm wavelength region, such as 193 nm and 157 nm. It is also desirable to provide photoresist compositions that employ photoacid generators.
Adamantane, the smallest member of the family of diamondoid compounds, is a highly condensed, exceptionally stable hydrocarbon compound. Adamantane and a range of adamantyl derivatives have been commercially available for years. This has made adamantane a regular substituent in a wide variety of families of chemical structures when a large, stable, bulky hydrocarbon moiety is desired. Adamantyl groups are found in polymers and are currently employed as constituents of positive photoresist materials.
Diamantane is also a highly condensed hydrocarbon compound. It is made up of two face-fused adamantane units. It can be synthesized but also occurs naturally in petroleum and can be isolated from various deep well hydrocarbon streams such as natural gas streams. A number of diamantane derivatives have been reported in the literature including a variety of mono and poly halides, mono- and dihydroxy materials, mono- and dicarboxylic acid derivatives, mono- and dialkynyls, and mono- and diamines. In addition, there are a number of diamantane-containing polymers in the literature but generally these materials appear to link the diamantane into the polymer through two or more links such that the diamantane forms an integral part of the polymer backbone.
We now desire to provide a family of derivatives of diamantane that can form polymers having pendant diamantyl groups. In addition, these derivative can contain additional functionality to impart desirable properties to the polymers they form.